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病毒和细胞 mRNA 特异性激活因子利用 PABP 和 eIF4G 来促进帽结合下游的翻译起始。

Viral and cellular mRNA-specific activators harness PABP and eIF4G to promote translation initiation downstream of cap binding.

机构信息

Medical Research Council Centre for Reproductive Health, Queen's Medical Research Institute, University of Edinburgh, Edinburgh EH16 4TJ, United Kingdom;

Medical Research Council Human Genetics Unit, University of Edinburgh, Western General Hospital, Edinburgh EH4 2XU, United Kingdom.

出版信息

Proc Natl Acad Sci U S A. 2017 Jun 13;114(24):6310-6315. doi: 10.1073/pnas.1610417114. Epub 2017 May 30.

Abstract

Regulation of mRNA translation is a major control point for gene expression and is critical for life. Of central importance is the complex between cap-bound eukaryotic initiation factor 4E (eIF4E), eIF4G, and poly(A) tail-binding protein (PABP) that circularizes mRNAs, promoting translation and stability. This complex is often targeted to regulate overall translation rates, and also by mRNA-specific translational repressors. However, the mechanisms of mRNA-specific translational activation by RNA-binding proteins remain poorly understood. Here, we address this deficit, focusing on a herpes simplex virus-1 protein, ICP27. We reveal a direct interaction with PABP that is sufficient to promote PABP recruitment and necessary for ICP27-mediated activation. PABP binds several translation factors but is primarily considered to activate translation initiation as part of the PABP-eIF4G-eIF4E complex that stimulates the initial cap-binding step. Importantly, we find that ICP27-PABP forms a complex with, and requires the activity of, eIF4G. Surprisingly, ICP27-PABP-eIF4G complexes act independently of the effects of PABP-eIF4G on cap binding to promote small ribosomal subunit recruitment. Moreover, we find that a cellular mRNA-specific regulator, Deleted in Azoospermia-like (Dazl), also employs the PABP-eIF4G interaction in a similar manner. We propose a mechanism whereby diverse RNA-binding proteins directly recruit PABP, in a non-poly(A) tail-dependent manner, to stimulate the small subunit recruitment step. This strategy may be particularly relevant to biological conditions associated with hypoadenylated mRNAs (e.g., germ cells/neurons) and/or limiting cytoplasmic PABP (e.g., viral infection, cell stress). This mechanism adds significant insight into our knowledge of mRNA-specific translational activation and the function of the PABP-eIF4G complex in translation initiation.

摘要

mRNA 翻译的调节是基因表达的一个主要控制点,对生命至关重要。至关重要的是,帽结合真核起始因子 4E(eIF4E)、eIF4G 和多聚(A)尾结合蛋白(PABP)的复合物使 mRNA 环化,促进翻译和稳定性。该复合物通常被靶向以调节整体翻译速率,并且也被 mRNA 特异性翻译抑制剂靶向。然而,RNA 结合蛋白对 mRNA 特异性翻译激活的机制仍知之甚少。在这里,我们解决了这一缺陷,重点研究了单纯疱疹病毒 1 蛋白 ICP27。我们揭示了与 PABP 的直接相互作用,足以促进 PABP 的募集,并且是 ICP27 介导的激活所必需的。PABP 结合几种翻译因子,但主要被认为作为 PABP-eIF4G-eIF4E 复合物的一部分激活翻译起始,该复合物刺激初始帽结合步骤。重要的是,我们发现 ICP27-PABP 与 eIF4G 形成复合物,并需要 eIF4G 的活性。令人惊讶的是,ICP27-PABP-eIF4G 复合物独立于 PABP-eIF4G 对帽结合的影响发挥作用,以促进小核糖体亚基募集。此外,我们发现细胞 mRNA 特异性调节剂Deleted in Azoospermia-like (Dazl) 也以类似的方式利用 PABP-eIF4G 相互作用。我们提出了一种机制,即各种 RNA 结合蛋白以非多聚(A)尾依赖性方式直接募集 PABP,以刺激小亚基募集步骤。这种策略可能与低腺苷酸化 mRNA(例如生殖细胞/神经元)和/或细胞质 PABP 有限(例如病毒感染、细胞应激)相关的生物学条件特别相关。该机制为我们对 mRNA 特异性翻译激活以及 PABP-eIF4G 复合物在翻译起始中的功能的认识增添了重要的见解。

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